1. Technical Field
The present invention relates in general to improved utilization of disk storage space in a hard disk drive and, in particular, to an improved method and apparatus for recovering previously unutilized load/unload zone real estate on the disks of hard disk drives.
2. Description of the Related Art
Generally, a data access and storage system consists of one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, one to six disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
A typical HDD also utilizes an actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
Typically, a slider is formed with an aerodynamic pattern of protrusions on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each platter and flies just over the platter's surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
In hard disk drives, load/unload (L/UL) designs are used to “load” the slider down from a ramp onto the spinning disk prior to any data reading and writing operations, and “unloaded” off of the disk back onto the ramp when the reading and writing operations are complete. As shown in FIG. 1, the area of contact on the disk surface is typically located adjacent to the outer radial edge 11 of the disk 13 and is known as the “load/unload zone” 15. Since the contact of the slider 17 with the disk can damage the disk, the load/unload zone 15 is not used to store data or for reading and writing operations. Load/unload zone 15 extends inward for a prescribed radial distance Z to an inner radial position 19. The first (radially outermost) read/write track 21 is located radially inward of inner radial position 19. Additional read/write tracks 25 are located radially inward of first track 21. Load/unload designs reduce the problems of head-disk stiction and media damage from shock as the fly height (e.g., the height at which a slider flies above the surface of a spinning disk) continues to decrease. These designs also have the advantage of reducing power consumption.
However, as stated previously, L/UL schemes potentially risk media damage from slider-disk contact during loading and/or unloading due to high disk speeds and high load/unload speeds. Research has shown that this damage is specifically associated with the sharp corners and/or edges of the block-like sliders digging into the disk surface upon impact. The resulting damage in the L/UL zone of the disk makes this region unsuitable for data storage, thereby reducing the overall storage capacity of the drive by 5 to 15%. Thus, an improved method and system for overcoming these problems to better utilize the L/UL zone is needed.